Rheostatic circuit-controlling apparatus



Dec. 31, 1929. J. G. ZIMMERMAN 1,741,802

RHEOSTATIC CIRCUIT CONTROLLING APPARATUS Filed April 21, 1923 2 Sheets-Sheet L Patented Dec. 31, I929 UNITED STATES PArsr OFFICE JAMES G. ZIMMERMAN, OF MILWAUKEE,

'WISCOHSIN, A$SIGNOR F ONE-HALF TO ALLIS-CHALMEERS MANUFACTURING COIHPAHY, A COEPURATION OF DELAWARE RI-IEOSTATIC CIRCUIT-CONTROLLING APPARATUS Application filed April 21,

1 vice disclosed in United States Patent No.

1,023,543, granted April 16, 1912. The general type of control device disclosed in the patent has-been demonstrated to be superior to those devices wherein relatively hard carv hon disks, arranged in series relation, are

utilized, and which depends upon a variation in the pressure exerted "upon and between the disks tosecu-re the desired resistance control; and this superiority is especially noticeable where it is desired to secure resistancecontrol over a wide range .and in a gradual manner.

The present invention contemplates an improved form of rheostatic controlling apparatus including a compressible resistance mediu-marranged between relatively movable circuit terminals, means being provided for securing such relative adjustment of the terminals as causes a variation in the density,

and hence the resistance, of the resistance medium; and such a device includes provisions for releasing or decreasing the density of the resistance medium, after it has been densely packed, so as to return it to its original loosely packed and fluent condition.

Embodiments of this invention may include instrumentalities associated with the resistance-varying device for short-circuiting the terminals at the point of minimum resistance in the devices, and for breaking the circuit through the device at the point of maximum resistance and embodiments of the invention likewise may include instrumentalities associated with the resistance-varying device, for

interrupting the circuit through the resistance-varying device independently of the ad justed condition .of the resistance-varying medium.

It is .an object of this invention to provide to an improved design and constructionof rheo- 1923. Serial No. 633,614.

static controlling apparatus embodying resistance-varying means and circuit-controlling means associated therewith.

It is a further object of this invention to provide an improved design and construction of rheostatic controlling apparatus of the character described wherein circuit-controlling means are effective to complete the normal circuit through the device independently of the adjusted condition of the variable resistance medium.

These and other objects and advantages are secured by the present invention, various novel features of which will be apparent from the description and drawings, disclosing embodiments of the invention, and will be more particularly pointed out in the claims.

In the accompanying drawings:

Fig. 1 is a sectional elevation of an embodiment of the inventiom'the sectional plane be-- ing that of the line I-I of Fig. 2. Fig. 2 is a sectional elevation in the plane of the line IIII of Fig. 1.

Fig. 3 is a sectional elevation of a modified embodiment of the invention, the sectional plane being that of the line IIIIII of F ig. d.

Fig. 4 is a sectional elevation in the plane of the line IV IV of Fig. 3.

Fig. 5 is a plan view of the device shown in Figs. 3 and 4.

Fig. 6 is a bottom view of the device shown in Figs. 3 and l.

Fig. 7 isa view similar to Fig. 1, showing a further modification, the plane of section being substantially through the axis of the operating rod, as indicated at VII of Fig. 8.

Fig. 8 is a view similar to Fig. 7 in a plane at right angles to the sectional plane of Fig. 7, as indicated at VIII of Fig. 7.

As disclosed in the drawings, a casing or housing 10 of insulating material, preferably of porcelain, is provided with a recess 12 in which is mounted a fixed terminal or contact 13 having its outer reduced end projecting through an aperture 14 in the rear wall of the casing. The reduced end of the terminal element is threaded and a nut 15 thereon cooperates directly, or through. the intermediary of the washer, with the rear wall of the casing to draw a shouldered portion 16 of the terminal. against the inner side of the rear wall of the casing or a washer thereon.

The recess 12 contains granular or powdered resistance material 17, preferably in the form of carbon, such as graphite or a mixture containing the same, a metal disk 18 being placed upon the powdered resistance medium, this metal disk having a'fairly close but readily slidable fit with the walls of the recess. A terminal head or contact 19 is provided at the inner or lower end of a rod or stem 21 having the portion adjacent the terminal threaded, as indicated at 23, for cooperation with a correspondingly and inte riorly threaded tubular portion or nipple 2% formed upon a front or cover plate 25 which encloses the recess and its contents. Due to the fact that the granular resistance medium consists of relatively fine particles and is of a quite fluid nature, it is advisable to provide a packing in the form of a washer 26 such as felt, at the inner side of the disk 18, and in contact with the wall of the carng, and, if desired, a protective bearing wz her 27, as of paper or hard fiber at the inner side of the felt washer. An annular insulating element or washer 28 is provided at the outer side of the disk 18, this washer being of relatively hard material and 0h. aperture therethrough readily permitting movement of the terminal head 19 therein.

The cover plate is held in operative position by means of screw bolts 31, 32 the inner side of whose heads bear against the cover plate, the bolts extending entirely through the wall of the casing to the rear side thereof where nuts 3% threaded on the ends of the bolts cooperate, either directly or through the intermediary washers, with therear wall of the casing to secure the cover plate in operative position. The outer ends of the screw bolt 32 and the terminal 13 serve as the circuit terminals for the device, wire connections being secured in operative position by means of nuts threaded upon the ends of these elements 32 and 13.

The metal disk 18 is urged toward the outer end of the recess 12 of the casing by means of a helical spring 37 hearing against the disk and the rear wall of the recess. This spring is preferably insulated, preferably by japan or shellac treatment. As indicated, the outer end of the spring bears upon the washer 27 and serves to maintain the felt washer in such cooperation with the metal disk 18 and the side wall of the recess so as to prevent loss of resistance material 17. This spring 37 readily works through the resistance medium 17 as the spring is compressed and extends during the operation of the device, and hence serves, during its extension, to unpack or loosen the granular resistance material after it has been previously packed or rendered dense.

The outer end of the rod 21 is provided with a handle 38, preferably of insulating material, which serves to adjust the'terminal head 19 on the rod into and out of the recess of the casing. Screws 39 cooperative with offset extensions or wings on the cover plate 25, are provided for securing the device in operative position relative to a support.

lVith the parts of the device as shown in Fig. 2, the circuit through the device is open, a break being indicated between the inner side of the terminal head 19 and the outer side of the metal disk 18 which acts as a terminal for the resistance 17.

As shown, the thickness of the terminal head is less than the thickness of the insulating spacing washer 28, and hence, when the terminal head is moved up into engagement with the under side of the cover 25 the required circuit-rupturing operation is insured between the terminal head and the disk 18. Adjustment of the handle 38 in the proper direction serves first to cause the terminal head 19 to contact with the metal disk 18, thus serving to complete the circuit through the device, from the terminal 32, through the cover plate 25, rod 23, terminal head 19, disk 18, granular resistance medium 17, and terminal 13. The resistance of this circuit is a maximum at this time for the resistance medium is loosely packed and occupies its greatest space. Further adjustment of the terminal head 19 in the same direction causes movement of the disk 18, acting as a plunger, into the recess, the disk serving to compress or compact the resistance medium and thus to both shorten the path between the disk 18 and the terminal 13 and also to render more dense, and hence more highly conductive, the resistance medium in this path. During this operation, the spring 37 is compressed and better serves to insure that the packing 26 closes the chamber against loss of resistance material. The physical dimensions of the parts are such that the resistance medium may compress to the extent required to permit the disk 18 to directly contact with the terminal 13, at which time these terminals serve to short-circuit the resistance path through the resistance medium, and hence the resistance of the circuit is a minimum.

During the reverse operation, that is, to increase the resistance of the circuit, as the terminal head is moved out of the chamber of the casing, the disk 18 remains in contact with and follows the head 19 in its movement, being forced in this direction by the spring 37. Continued adjustment of the device in this direction to separate the terminals, brings the disk 18 into contact with the under side of the insulating spacer 28. At this time the resistance of the path between the fixed terminal 13 and the disk 18 is a maximum, the granular resistance material being returned to its initial loosely packed and fluent condition through the action of the spring 37 as the compression thereon is released. Further adjustment of the operating rod 21 serves to move the terminal head away from the disk 18 and into engagement with the under side of the cover plate 25, this latter operation serving to break the circuit through the device.

With this combination, the resistance of the circuit may be gradually and substantially uniformly increased throughout practically the entire stroke of the terminal disk 18, and there is substantially no lag in the resistance values, on the return or resistanceincreasing stroke, with respect to the values corresponding to the same positions or adjustments of the terminal head 19 during the entering or resistance-decreasing stroke. Again, because of the relatively long stroke, and the fact that operation of the head 19 and the terminal disk 18 is secured through the action of a relatively fine screw, the

variation in resistance values may be ex-" tremely gradual, being substantially a vernier adjustment, between the limiting positions of the terminal disk 18 and the head 19 and its actuating rod.

In Figs. 3, 4, 5 and 6, there is disclosed a modification embodying means for interrupting and completing the circuit through the resistance-varying device independently of the position of adjustment of the terminal head 19, and hence the resistance of the path between the disk 18 and the terminal 13, through the granular resistance medium. This construction readily permits retaining in satisfactory adjustment the resistance through the granular resistance medium, and at the same time permits making and break ing of the circuit through the device.

As disclosed, a metallic frame 42 of the general design shown, is provided, an aperture 43 in the upper arm 44 of this frame being in position to receive the screw bolt 82. an insulating washer 45 with a nipple former thereon surrounding the upper end of the screw bolt 32 and electrically separating the bolt from the frame 42 and the cover plate The inner end 46 of the upper arm 44 of the frame is formed along an arc of a circie for direct engagement with the outside of the bushing or nipple 24 on the cover plate, this cooperation between the parts serving to pre vent rotation of the frame 42 upon the screw bolt 32. The lower arm 47 of the frame 42 has its end square and in substantial engagement throughout with the outer wall of the casing 10, as indicated at 48.

A metal rod or stem 49 projects throughalined apertures in the upper and lo 'er arms of the frame, the lower end of the rod 49 being turned at right angles to the top portion, as indicated at 51. Steps 52 and 53 are formed integrally with the lower arm 47, preferably by being pressed therefrom, these stops serving, with the portion 51, to limit the rotary movement of the rod. A contact element 54, in the form of a leaf spring has its lower portion. bent at an angle to its body portion andapertured to permi mounting upon the lower end of the screw bolt 32 between the nut 34 and the wall of the casing 10, as indicated. This leaf spring 54 is biased to the position-indicated in Fig. 4, and it is so arranged relative to the bent portion 51 of the rod 59 as to be fully engaged in electrically conductive relation by the end of the element 51 when the latter is in engagement with the stop 58, there being sufiicient resilience in the contact 54 to insure proper electrical contact. When the rod 49 is operated to shift the element 51 into engagement with the stop 52, the cooperative parts are moved out of contact relation, the spring contact 54 moving to its initial position, as indicated in Fig. 4.

The rod 49 is held against longitudinal movement out of operative position by means of an integral projection 56 on the rod hearing directly, or through the intermediary of i a washer, upon the outer side'of the upper arm 44 of the frame 42. In order to steady the rod and impart thereto the required spring or snap action during operation to open and closed positions, an integral projection 57 at the lower side of the arm 49 of the frame is resiliently engaged by this element 51, the latter riding over the projection as it moves from one position to the other and substantially leaving the projection at the end of its travel. Through this cooperation, the projectio'n constitutes a stop which serves to maintain the rod and the auxiliary switch in adjusted open or closed position. A handle 58, preferably of insulating material, is mounted upon the upper end of the rod 49, preferably by being screw threaded thereon. An indicating pointer 59 may be fixedly secured in adjusted position relatively to the rod to give a desired. indication of the open or closed position of the switch device composed of the cooperative contact elements 51 and 54. The preferable arrangement is to clamp this indicating pointer between the under side of the handle 58 and the upper side of a nut adjustable on the threaded end of the rod 49.

The resistance-varying operation of the rod 21 and its terminal head 19 of this device may be the same as that of the device shown in Figs. 1 and 2. between the two devices is that instead of having a circuit between the positive terminal and the cover plate completed directly by the screw bolt 32, as in Figs. 1 and 2, this circuit is now from the terminal end of the screw bolt through the spring contact 54 and the switch element 51, the body portion of the rod the frame 42, to the cover plate with which the frame is in direct contact. As will be apparent, the rod 49 may readily be ad- The essential difference justed to open or close the circuit through the resistance-varying device at any time, in dependently of the adjustment of the resist ance device.

The modification in Figs. 7 and 8 is substantially the same as shown in Figs. 1 and 2 as to the features of the resistance-varying device; but an auxiliary make and break device, for securing the function present in the apparatus of Figs. 3 and 4, is incorporated in the modified device in such a manner as to produce a more nearly unitary device. As indicated the operating rod 19 is provided with a central bore 61, this bore being interiorly threaded for cooperation with the threaded portion of an auxiliary rod 63 having its lower end formed as a terminal for engagement with the upper side of the metal disk 18. An auxiliary handle 65, preferably considerably smaller than the handle, is mounted upon the upper end of the rod 63 and serves to move the lower contact end 64 of the rod into and out of engagement with the upper end of the contact 18. Instead of being in direct contact with the disk 18, the terminal head 19 is separated therefrom by an insulating barrier in the form of a washer 67 havin a central aperture sufficiently large to permit movement therethrough of the lower contact end 64c of the rod 63. lVith the parts in the position indicated in Fig. 8, it will be obvious that the resistance of the path through the granular resistance medium may be adjusted in the same manner as with the device of Figs. 1 and 2. Independently of the position or condition of adjustment of the resistance-varying device, the circuit through the device may be interrupted or completed by merely moving the contact end 64 of the rod 63 out of or into engagement with the disk 18. This action Will be readily apparent, for the 7 normal circuit through the resistancevarying device is completed between the rod 23 and the terminal disk 18 only through the intermediary of the contact end of the rod 63. The pitch of the threads on the inner and outer surfaces of the rod 21 may be different to facilitate adjustment of the position of one of such rods without interfering with the adjustment of the other rod.

It should be understood that the invention claimed is not limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

It is claimed and desired to secure by Letters Patent:

1. In a rheostatic circuit-controlling device, a housing containing a compressible resistance medium and having a cover element at one side, a fixed terminal within said housing, a movable terminal within said housing, means for actuating said movable terminal,

5 said actuating means being supported by and adjustable relative to said cover element, and

means operatively associated with said cover element for arresting the movement of said terminal in a resistance-increasing direction, said actuating means being movable away from said movable terminal to break the circuit through the device when said movable terminal is held by said arresting means.

2. In a rheostatic circuit-controlling device, a housing carrying a variable resistance medium, actuating means for causing variation of the resistance of said medium, a cover plate for the open side of said housing, said actuating means being carried by and adj ustable relative to said cover plate, and a bolt for securing said cover plate in position, said bolt extending through said housing to the opposite side thereof and constituting at said latter portion a line terminal, the operative relation between said movable terminal and said resistance medium permitting relative separation for circuit-breaking purposes.

In testimony whereof, the signature of the inventor is aflixed hereto.

JAMES G. ZIMMERMAN. 

